He sends down from the sky, rain, and valleys flow according to (13:17)

﴿أَنزَلَ مِنَ السَّمَاءِ مَاءً فَسَالَتْ أَوْدِيَةٌ بِقَدَرِهَا فَاحْتَمَلَ السَّيْلُ زَبَدًا رَّابِيًا ۚ وَمِمَّا يُوقِدُونَ عَلَيْهِ فِي النَّارِ ابْتِغَاءَ حِلْيَةٍ أَوْ مَتَاعٍ زَبَدٌ مِّثْلُهُ ۚ كَذَٰلِكَ يَضْرِبُ اللَّهُ الْحَقَّ وَالْبَاطِلَ ۚ فَأَمَّا الزَّبَدُ فَيَذْهَبُ جُفَاءً ۖ وَأَمَّا مَا يَنفَعُ النَّاسَ فَيَمْكُثُ فِي الْأَرْضِ ۚ كَذَٰلِكَ يَضْرِبُ اللَّهُ الْأَمْثَالَ﴾
[ الرعد: 17]

13:17 He sends down from the sky, rain, and valleys flow according to their capacity, and the torrent carries a rising foam. And from that [ore] which they heat in the fire, desiring adornments and utensils, is a foam like it. Thus Allah presents [the example of] truth and falsehood. As for the foam, it vanishes, [being] cast off; but as for that which benefits the people, it remains on the earth. Thus does Allah present examples.

Allah strikes an example of the erosion of falsehood and the survival of truth with rainwater that comes down from the sky and causes riverbeds to flow, each according to its size, whether big or small.
The overflowing water carries on its surface scum and froth that rise above the water.
He then gives another example of falsehood and truth with some of the metals that people put into a furnace in order to melt down and to make ornaments for people.
Falsehood is like the scum and froth that floats above the water and like the slag expelled by smelting the metal.
Truth is like the pure water that can be drunk and that causes fruits, grass and vegetation to grow; and like the metal that remains after smelting, which is of benefit to people.
Just as Allah has given these two examples, He gives many examples to people so that truth may be distinguished from falsehood.

He sends down water (rain) from the sky, and the valleys flow according to their measure, but the flood bears away the foam that mounts up to the surface, and (also) from that (ore) which they heat in the fire in order to make ornaments or utensils, rises a foam like unto it, thus does Allah (by parables) show forth truth and falsehood. Then, as for the foam it passes away as scum upon the banks, while that which is for the good of mankind remains in the earth. Thus Allah sets forth parables (for the truth and falsehood, i.e. Belief and disbelief).

phonetic Transliteration

Anzala mina alssamai maan fasalat awdiyatun biqadariha faihtamala alssaylu zabadan rabiyan wamimma yooqidoona AAalayhi fee alnnari ibtighaa hilyatin aw mataAAin zabadun mithluhu kathalika yadribu Allahu alhaqqa waalbatila faamma alzzabadu fayathhabu jufaan waamma ma yanfaAAu alnnasa fayamkuthu fee alardi kathalika yadribu Allahu alamthala

Abdullah Yusuf Ali - Translation

He sends down water from the skies, and the channels flow, each according to its measure: But the torrent bears away to foam that mounts up to the surface. Even so, from that (ore) which they heat in the fire, to make ornaments or utensils therewith, there is a scum likewise. Thus doth Allah (by parables) show forth Truth and Vanity. For the scum disappears like forth cast out; while that which is for the good of mankind remains on the earth. Thus doth Allah set forth parables.

Safi-ur-Rahman al-Mubarakpuri

He sends down water from the sky, and the valleys flow according to their measure, but the flood bears away the foam that mounts up to the surface - and (also) from that (ore) which they heat in the fire in order to make ornaments or utensils, rises a foam like unto it, thus does Allah (by parables) show forth truth and falsehood. Then, as for the foam it passes away as scum upon the banks, while that which is for the good of mankind remains in the earth. Thus Allah sets forth parables.

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